Wax emulsions have been used in composite wallboard (e.g., gypsum wallboard) for many years. For example, wax emulsions sold under the trade name AQUALITE® by Henry Company, and several wax emulsion formulations are disclosed in the prior art, such as U.S. Pat. No. 5,437,722.
Gypsum is employed in a gypsum panel or board product known as wallboard which is widely used as a structural building panel. Gypsum products may be produced by mixing anhydrous calcium sulfate or calcium sulfate hemihydrate with water and allowing the mixture to hydrate or set as calcium sulfate dihydrate, which is relatively hard. Gypsum wallboard may comprise a panel-like core of set gypsum sandwiched between a pair of paper liners which form the exposed outer surfaces of the wallboard. Fiberglass liners have also been used. In many applications wallboard is exposed to water. A problem with set gypsum is that it absorbs water, and such absorption reduces the strength of the wallboard.
Further, in order to achieve a smooth, visually appealing surface, the joints between boards, cracks, screw holes, and/or nail holes must be concealed. Conventional wallboard joint compounds are commonly used to cover and finish gypsum wallboard joints, cornerbead, and screw or nail holes. Joint compounds can be spread over mesh or tape used to connect wallboards. It may also be used to patch and texture interior walls.
The intrusion of water through wall spaces, either through prolonged direct contact or via high humidity, has a debilitating effect (mold and structural damage) on standard wall systems. It is for this reason that moisture resistant wallboard, passing ASTM C473, was developed. An integral part of the wall system is the tape joint compound which, so far, has no accepted standards for water resistance.
Some specially formulated gypsum wallboards (also called “Green” boards) contain a water repellent additive such as a wax emulsion to impart the added functionality of water resistance to the board. While such “green” gypsum wallboards meet strict water repellency performance requirements (ASTM C473), there are no such requirements and indeed, no ready-mix joint compound that offers commensurate water repellency. Consequently, the ready-mixed joint compound is a severe vulnerability in existing wall systems where protection against water damage is crucial. The result of water seepage through joint compound to the studs on the other side of the wall ultimately has devastating structural and microbial implications for the wall system, first by absorption of the seeped water into the wood studs followed by their swelling and deformation (leading to expensive structural problems) and then, the creation of a fertile ground for rapid mold growth. Conventional ready mixed joint compound is therefore a weak link in the long term microbial resistance and integrity of the wall system.